1. Field of the Invention:
The present invention is directed toward an indexing mechanism for a multiple objective nosepiece of an optical instrument, such as a microscope. The indexing mechanism provides for repeatedly accurate alignment of each individual objective with the optical axis of the instrument and for friction-free rotational movement of the nosepiece when changing objectives.
The indexing mechanism also may be connected to a source of electrical energy and utilized as a switch to control an electrical function of the instrument or accessory associated therewith.
2. Description of the Prior Art:
The characteristics of a microscope nosepiece which has multiple objectives are that (1) it should be able to provide for repeatedly accurate alignment of the selected objective with the optical axis of the instrument, (2) there should be positive locking location of the nosepiece when the selected objective is axially aligned, (3) there should be essentially very little torque involved to rotate the nosepiece to change objectives, and (4) the nosepiece and cooperating indexing mechanism should be fairly simple to construct and maintain, resulting in relatively low manufacturing and servicing costs.
The constant problem of providing positive and accurate alignment of each objective with respect to the instrument's optical axis has been addressed many times over by a wide variety of construction methods.
One such solution was proposed by C. J. Bowerman in U.S. Pat. No. 3,656,759, which issued Oct. 27, 1953. In this apparatus, a detent mechanism operates between the stationary support arm and the rotatable nosepiece of a microscope. Essentially, the mechanism provides for a rounded button which is pressed into engagement against the peripheral edge of the nosepiece by a flat spring which is mounted to the support arm. The button and spring assembly act as the detent member when received within shallow slots formed in the edge of the nosepiece.
A further apparatus, shown by B. W. Jones in U.S. Pat. No. 2,621,563, issued Dec. 16, 1952, utilizes a construction similar to the device of Bowerman.
The above-referenced devices generally suffer from similar problems. The detenting mechanism has, in each application, a non-rotatable button or ball mounted to a leaf spring. The non-rotatable ball is biased into engagement against a complementing surface on the nosepiece shell. A plurality of raised ramps is formed on the surface such that as the nosepiece shell is rotated, the ball engages the ramps. Continued rotation of the nosepiece shell forces the spring to flex and the ball to slide along the ramp until it reaches the detent. The spring then forces the ball into the detent. The action of sliding the ball along the surface of the nosepiece creates unwanted friction. Further, because of the friction, parts are caused to wear. The friction drag and the wearing have been endured for lack of a better system.
These systems further suffer from the inherent problem that operators may frequently apply more torque to the nosepiece shell than necessary and, consequently, rotate past the desired objective. This happens because the rotation of the nosepiece shell between detents is easily accomplished whereas when a detent is initially encountered frictional drag becomes very noticeable. To overcome this situation the operator applies more torque. Frequently, this additional torque causes over-rotation as the point contact formed between the ball and shallow detent slot is not sufficient to stop the nosepiece shell from rotating.
The detenting system shown by Bowerman has a further disadvantage in that it is mounted externally so that it is directly exposed to dust and other foreign debris which cause additional friction and premature wear.
Another indexing mechanism is disclosed by T. G. Aitcheson in U.S. Pat. No. 2,565,419 issued Apr. 21, 1951. In this apparatus a spring arm is mounted to the inner wall of a microscope turret housing. The spring arm carries a small roller which engages any one of a plurality of V-shaped notches which are formed in the periphery of the carrier. When the carrier is rotated the roller is forced outwardly by the notch and rolls along the periphery of the carrier.
The system suffers from the problem that unless the roller and the axle to which it is mounted are perfectly concentric with each other, par-centration will be extremely difficult to achieve. That is, the error between the roller and axle will transfer to the carrier which results in unacceptable error in the optical alignment. This arrangement has a further drawback in that the roller is small and the V-shaped notch is correspondingly small, over-rotation of the carrier is likely to happen. An additional drawback is there is only one point contact made between the roller and the notch. Also, because the wheel is rotatably mounted to the spring it may easily be forced from the notch, perhaps by an inadvertent bump to the carrier.
The invention, as set forth and described hereinafter, overcomes these problems, as well as others, encountered in optical instruments, such as microscopes.